Lethal Violence in Chimps Occurs Naturally, Study Suggests

Are chimpanzees naturally violent to one another, or has the intrusion of humans into their environment made them aggressive?

A study published Wednesday in Nature is setting off a new round of debate on the issue.

The study’s authors argue that a review of all known cases of when chimpanzees or bonobos in Africa killed members of their own species shows that violence is a natural part of chimpanzee behavior and not a result of actions by humans that push chimpanzee aggression to lethal attacks. The researchers say their analysis supports the idea that warlike violence in chimpanzees is a natural behavior that evolved because it could provide more resources or territory to the killers, at little risk.

But critics say the data shows no such thing, largely because the measures of human impact on chimpanzees are inadequate.

While the study is about chimpanzees, it is also the latest salvo in a long argument about the nature of violence in people.

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Debate surrounds whether chimpanzees are naturally violent to one another or if the intrusion of humans has played a role.CreditIan Gilby

In studying chimpanzee violence, “we’re trying to make inferences about human evolution,” said Michael L. Wilson, an anthropologist at the University of Minnesota and a study organizer.

There is no disagreement about whether chimpanzees kill one another, or about some of the claims that Dr. Wilson and his 29 co-authors make.

The argument is about why chimpanzees kill. Dr. Wilson and the other authors, who contributed data on killings from groups at their study sites, say the evidence shows no connection between human impact on the chimpanzee sites and the number of killings.

He said the Ngogo group of chimpanzees in Uganda “turned out to be the most violent group of chimpanzees there is,” even though the site was little disturbed by humans.

They have a pristine habitat, he said, and “they go around and kill their neighbors.”

Robert Sussman, an anthropologist at Washington University who supports the idea that human actions put pressure on chimpanzee societies that results in killings, was dismissive of the paper. “The statistics don’t tell me anything,” he said. “They haven’t established lack of human interference.”

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Titan, an adult male from one of the communities included in a new study about violence among chimpanzees and bonobos.CreditIan Gilby

Brian Ferguson, an anthropologist at Rutgers University who has written extensively on human warfare and is working on a book about chimpanzee and human violence, also argued that the measures of human impact were questionable. The study considered whether chimpanzees were fed by people, the size of their range and the disturbance of their habitat. But, Dr. Ferguson said, impact “can’t be assessed by simple factors.”

“I’m arguing for the opposite of the method that’s being used here,” he said, adding that a detailed historical analysis was needed for each site.

Behind the discussion of violence among chimpanzees is a long-running dispute over whether chimpanzee behavior offers insights about human behavior.

Richard Wrangham of Harvard, the senior author of the new paper and Dr. Wilson’s onetime doctoral adviser, is the co-author of a 1996 book, “Demonic Males: Apes and the Origins of Human Violence.” Although the issue is not mentioned in this paper, he argues that chimpanzee behavior “is a reasonable start for thinking about primitive warfare in small-scale societies.” But, he added, “I certainly wouldn’t want to say that chimps have anything much to say directly about what’s going on in Syria.”

Dr. Sussman, who is skeptical of drawing connections between chimpanzee and human violence, said, “War has nothing to do with what chimpanzees do.”

A version of this article appears in print on , on Page A18 of the New York edition with the headline: Lethal Violence in Chimps Occurs Naturally, Study Suggests. Order Reprints | Today’s Paper | Subscribe

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